Iron-aluminum-silicon-titanium alloy



United States Patent 3,206,304 IRON-ALUMDIUM-SILICON-TITANHHVI ALLOY Max F. Bechtold, Kennett Square, Pa., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware No Drawing. Filed Aug. 14, 1962, Ser. No. 216,747 11 Claims. (Cl. 75124) This application is a continuation-in-part of application Serial No. 832,757, filed August 10, 1959, now abandoned.

This invention relates to novel compositions of matter containing aluminum, iron, silicon and titanium (by ele mental analysis) as their essential ingredients and to alloys and shaped objects prepared from such compositions that are strong, dimensionally stable and resistant to oxidation even at high temperatures.

Much eifort has been expanded in search of metals or alloys which possess unexpected combinations of properties essential to or generally desirable in specific fields of use. Particularly is this true with respect to metals or alloys that can be subjected to high temperatures in air without deleterious effects such as substantial loss of strength, warpage or oxidation. The aluminumiron-silicon-titanium alloys and shaped objects (hereinafter, sometimes referred to as shapes or objects) of the present invention do possess a combination of properties and characteristics which render them of considerable value in a number of fields of use. It is, therefore, to be understood that the alloys and objects hereinafter more fully described are not to be considered as restricted to any particular field of use. However, their outstanding and unexpected properties at temperatures above about 900 C. render them especially useful at such temperatures; and therefore, the products of the present invention will be described primarily with respect to this use although not intended to be limited thereto.

It is an object of the present invention to provide compositions of matter (hereinafter referred to as precursor compositions) containing readily available and inexpensive constituents, which are easily converted by known techniques, e.g., cold-pressing and firing, slip-casting and firing, hot-pressing or melt-casting, to alloys and shapes having outstanding properties at temperatures above about 900 C. Another object of this invention is to provide alloys having as their basic and essential characteristics good strength, dimensional stability and resistance to oxidation at temperatures above 900 C., thereby rendering them useful at such temperatures as load-bearing structural materials. A further object is to provide shaped objects, including objects of ultimate use, of any shape, which have the properties of the alloys of this invention and can be prepared from the precursor compositions either directly by the above-mentioned known techniques or indirectly by machining or otherwise shaping such alloys.

The above and other objectives of this invention are attained by precursor compositions, alloys and shaped objects containing as their essential ingredients (on the basis of elemental analysis) 3-15 aluminum, 6088% iron, 3-8% silicon and 6-25 titanium, by Weight. It is to be understood that the range of weight percent for each element represents its percentage of the total amount of aluminum, iron, silicon and titanium present in the products of the invention and not is percentage of the gross composition thereof. Thus, the sum of the amounts of these individual elements must equal 100%.

Element(s) or compound(s) in addition to aluminum, iron, silicon and titanium may be present in the alloys Patented Sept. 14, 1965 and shaped objects, and thus in the precursor compositions, provided they do not have a substantial adverse elfect upon the strength, dimensional stability and oxidation resistance of the AlFeSi-Ti system (i.e., the systern consisting of these four elements in the above proportions), at a temperature above about 900 C. Various impurities, i.e., ingredients other than aluminum, iron, silicon and titanium, which are present in minor amounts in the commercially available starting materials can be tolerated, as can added amounts of other element(s) and compound(s) which will not affect the desired combination of properties to a degree sufficient to make the alloys and shaped objects undesirable as load-bearing structural materials or objects at a temperature above about 900 C. Also, there may be added such amounts of element(s) and/ or compound(s) which will impart to the alloys and objects in an anticipated manner, various properties that are desirable for special applications without having a material adverse effect upon their above-mentioned high temperature characteristics, or even having a beneficial effect on some or all of such characteristics.

It is to be understood that minor changes in the relative proportions of the essential elements will occur when the precursor compositions are converted to alloys or shaped objects due to the elimination of expendable impurities in the starting materials. However, for simplicity of expression and ease of understanding, the proportions of essential elements in the precursor compositions and in the alloys and shapes of this invention are referred to in terms of the same numerical values.

If desired, the strength and electrical resistance of the alloy and shaped objects at high temperatures may be increased by admixing Al O in the precursor composition before it is converted to the alloy or shaped object, Such modified precursor compositions, alloys and objects constitute another aspect of this invention. The Weight ratio of alumina to A1FefiSiTi should not exceed 90:10 and preferably lies in the range 5:95 to 90:10. The A1 0 modified alloys and objects possess superior insulating properties when the ratio of alumina to Al-Fe-Si-Ti is above :30, preferably at least :20. Thus, A1 0 is an example of a compound which may be added to the Al Fe$iTi system, even in major proportions, to impart thereto an expected property, i.e., electrical resist ance, and at the same time improve the overall high temperature strength of the alloy.

As was noted above, the alloys and shaped objects of this invention are characterized by good strength, dimensional stability and oxidation resistance at temperatures above about 900 C., e.g., up to about 1000 C. It is particularly out-standing that most of the alloys and objects possess this combination of properties at temperatures between about 1000 C. and 1300C., with some being useful as dimensionally stable, load-bearing structural materials or objects at temperatures up to 1500 C. and even higher.

The strength of the alloys and shaped objects is determined by considering together their impact and transverse rupture strengths. The primary value of the alloys and objects of this invention is that in general they have a strength which approaches or surpasses that of most super alloys at temperatures above about 900 C. in combination with outstanding dimensional stability and oxidation-resistance, including resistance to scale formation. The superior dimensional stability and oxidation resistance of the products of the subject invention, as measured by Weight gain (AW) and cumulative percentage change in linear dimensions (AD), respectively, is apparent from the many examples hereinafter set forth.

Although all alloys and shaped objects having compositions falling within the ranges described above possess the desirable high temperature properties just described, certain of these compositions are particularly outstanding with respect to one or more specific high temperature properties. For example, alloys containing a maximum of 18% titanium usually exhibit higher oxidation resistance and dimensional stability at 1100- 1300 C. than those containing larger proportions of titanium. If high temeprature oxidation resistance is improved by the introduction of larger proportions of Si or A1 at the expense of Fe, impact strength suffers and the melting point is lowered. Hence, for impact resistant alloys and objects, an iron content of at least 60%, preferably 70%, is employed. Alloys which have high impact strength, useful load-bearing capacity above 1000 C. and high oxidation resistance at temperatures in the range of 11001300 C. contain 7l4% Al, 65-80% Fe, 48% Si and 6l5% Ti. The best balance of properties is obtained in alloys containing 714% Al, 70-80% Fe, 4-8% Si, and 6-15 Ti. These alloys are magnetic, do not soften at temperatures below about 1300 C., and when exposed to air at about 1200 C. acquire a very thin adherent coating having an appearance similar to that of stain-finished aluminum. With alloys obtaining 70-80% Fe, outstanding impact strength is obtained without appreciably sacrificing oxidation resistance and dimensional stability when the silicon content is limited to 36% and the aluminum and titanium contents are in the ranges 844% and 6-18%, respectively.

In preparing the alloys and shaped objects of this invention the elements themselves or compounds and alloys thereof can be employed. For example, the alloy compositions can be prepared by heating together aluminum, iron, silicon and titanium in such proportions that the final composition falls within the ranges cited above. Alternatively, ferro-titanium, iron-aluminum alloys, titanium disilicide, silico-titanium alloys, iron-silicon alloys, and the like can be employed to provide part or all of the constituent elements.

When powder metallurgy techniques are employed to convert the precursor compositions to alloy-s or objects, the starting materials should be in the form of a fine powder having substantially all particles (i.e., at least 95% by weight) less than 75 microns in size and should be thoroughly mixed to insure homogeneity. It is preferred that less than 2% of such coarse grains be present. It is still better to screen out all coarse particles since they serve as points of chemical and mechanical inhomogeneity. Suitable powders are readily obtained by mixing fine commercial powders or by milling or dry-grinding coarser raw materials by conventional methods until the desired particle size is achieved. The progress of the grinding or milling may be followed by usual microscopic techniques.

Commercial powdered forms of aluminum, iron, titanium, titanium disilicide, and silico-titanium, which are available with primary particle sizes less than about microns, and ferrosilicon and ferrotitantium, which are usually much coarser 0A to ZOO-mesh), are suitable for use in preparing the compositions of this invention.

The dry powders prepared as above can be given any desired shape, e.g., by cold-pressing, extrusion with or without previous cold-pressing, or by slip-casting and drying. The shaped powder compositions which contain water or other volatile liquids should be dried before heat treatment to a liquid content of less than about 3% to prevent rupture of the object during firing. It is preferred that the shaped objects be no less than about 1 mm. in minimum dimension since thin objects are not only difilcult to obtain, but if obtainable, have low structural strength and are more subject to oxidation during firing than thicker objects.

The shaped powder compositions are converted into solid alloys by firing at a temperature of at least 900 C.,

preferably 1100-1300 C. The alloying reaction is exothermic and should be controlled so that the maximum temperature does not exceed that at which the alloy loses its dimensional stability. The optimum temperature depends upon the exact composition of each powder compact, the properties desired and the heating method, and may be readily determined by preliminary tests.

Hot pressing may also be employed to convert such powders to alloys or objects. Hot-pressing is carried out at a pressure of at least 1000 p.s.i. and a temperature of 900 C. or above. Particularly useful products are obtained by hot-pressing at 1200l300 C. under 2000- 5000 p.s.i. pressure.

In the preparation of products containing large amounts of A1 0 the heat given off by the alloying reaction is relatively small and rapid sintering in air may be diificult. Such products may be fabricated by sintering in inert atmospheres, hot-pressing or electrical flash sintering. In general, powder compositions containing the A1 0 require higher firing temperatures, i.e., up to 1600 C.

The time of heating the powder compositions at the alloying temperature must be sufficient to insure complete conversion to the alloy. Times of 30 seconds to 30 minutes usually suffice although longer periods may be employed if desired without detrimental effect. It is sometimes desirable to carry out a preliminary firing of the powder composition under the conditions described above and then to grind the fired material to fine particle size and hot press into the form of the final object.

An alternative but less preferred method of preparing the alloys and objects of this invention is by melting and cast-ing at a temperature above 1300 C., usually 1400- 1700 C. When this method is employed, the particle size of the constituent materials in the precursor composition is not critical and relatively massive forms such as lumps can be employed. The precursor composition in its molten state can be cast into a mold of any desired dimensions to prepare ingots, bars, rods, machine parts and other shaped objects.

The invention is illustrated in greater detail by the examples which follow. In these examples, quantities are referred to in parts by weight of the elements and A1 0 actually present in the precursor composition. Transverse rupture strength is measured using a specimen nom inally 2" long and A" x A" in cross-section supported symmetrically on parallel ceramic rods 4;" in diameter and 1" apart. Force is applied at the center of the portion of the bar between the supports by the edge (radius A of a V-shaped member.

Impact strength is measured by a modification of ASTM Method E-2347T using unnotched specimens 1" x A" x A" in nominal dimensions. These specimens usually are prepared from pieces resulting from previous transverse rupture tests. In impact testing, half the length of the specimen is unsupported and the point of impact is 0.3" from the support. A 25 inch-pound hammer is usually employed.

EXAMPLE I A mixture containing 50 g. of 40% ferrotitanium powder (analysis: 7.2% A1, 47.86% Fe, 3.38% Si, 40.19% Ti, 137% other elements), 34.48 g. of iron-silicon alloy (84% Fe, 14.5% Si, 0.85% C, 0.65% Mn) and 15.52 g. of reduced Fe powder was dry-milled for approximately 18 hours at 85 rpm. in a 250 cc. porcelain ball-mill containing 12 porcelain cylinders measuring x A". This mixture contained Al, Fe, Si, and Ti in the proportions 3.6:68.4:6.7:20.1. The resultant powder was passed through a ZOO-mesh screen to remove any particles larger than microns in size. A portion was then pelleted at 40 tons/sq. in. pressure and the pellet placed in a furnace (in air) at 1200 C. The pellet attained 1200 C. in

16 seconds and a maximum temperature above 1200 C. in 36 seconds. After 2 minutes in the furnace, the pellet was removed and quenched in water at room temperature. The fired pellet was hard, metallic, responsive to a magnet, porous and difficult to fracture by hitting with a hammer.

Another portion of the above powder was cold-pressed at 18 tons/sq. in. into the form of a rectangular bar. This bar was fired for 2 minutes in air at 1300 C. A calorescent reaction occurred and a maximum temperature above 1300 C. was reached in 39 seconds. The product was a glazed, hard, bright metal bar having a bulk density of 5.15 g./cc., which exhibited good impact strength.

A further portion of the above powder was ball-milled for an additional 16 hours as described above. The resultant finer powder was pressed in a graphite die for 20 minutes at 1300 C. under 4000 psi. pressure.

The bar so produced was ground to remove surface irregularities and subjected to physical testing. The bar had a bulk density of 5.93 g./cc. and exhibited a transverse rupture strength in air at 1000 C. of 39,260 p.s.i. The impact strength measured on portions of the specimen used in the transverse rupture strength test was 40.7 ft. lb./sq. in. (average of two determinations). Knoop hardness values at 1000 g., 100 g. and g. loads, respectively, were 855, 985 and 1706. A portion of the bar was subjected successively to temperatures of 500, 600, 700, 800, 900, and 1000 C. in air for 16 hours at each temperature. After each heating period, the specimen was cooled, measured and weighed. After the entire series of heat-treatments, the cumulative change in linear dimension (AD) was 3.24% and the total gain in weight (AW) was 1.95%.

EXAMPLE II Iron powder (270 g.), titanium powder (48 g.), aluminum powder (30 g.), and silicon powder (12 g.) were mixed and ball-milled for 24 hours at 80 r.p.m. in a l-qt. porcelain ball-mill containing twenty-five, x A porcelain cylinders. The resultant fine powder was screened through 200-mesh, the coarse grains (0.3%) being discarded. A portion of the powder was pelleted as in Example I and fired in air in the full flame of an oxygen/gas torch. There ensued immediately a calorescent reaction in the pellet, during which the torch flame was momentarily withdrawn. When the calorescence had subsided, heating was resumed. The total heating time was two minutes. The resultant pellet was fractured with difficulty with a hammer, and found to be a slightly porous, but strong bright metal.

EXAMPLES III-VII These examples illustrate the preparation of precursor compositions and alloys of this invention using various 6 compounds and alloys of the elements as starting materials. The Fe-Si alloy referred to in these examples con tains 84% Fe, 14.5% Si, 0.85% C. and 0.65% Mn. The preparation of the precursor compositions and their conversion to alloy objects by hot-pressing were carried out as described in Example I. Details of the preparation are shown in Table A below and the properties of the final alloys are described in Table B.

In all the examples of Table B, oxidation resistance is determined by heating the sample in air successively at l000, 1l00, and 1200 C. for 16 hours at each temperature. After each heating period, the sample is cooled to room temperature, weighed and measured. Cumulative changes in linear dimensions (AD) and weight (AW) after the heating periods at 1000 and 1200 C. are shown. In some cases, the samples have been heated at various temperatures between 500 and 900 C. prior to the higher temperature tests. Oxidation at temperatures below 1000 C. is insignificant.

EXAMPLES VIII-XVI These examples illustrate the preparation of the precursor compositions of this invention using the free elements as starting materials. The preparation of the precursor compositions and their conversion to alloy objects by hot-pressing were carried out as described in Example I. Details of the preparation are shown in Table A below and properties of the alloy products in Table B. Analytical data on a second bar of the composition of Example XI prepared at a mold temperature of 1275 C. were 10.67 Al, 74.18 Fe, 4.32 Si, 9.60 Ti, 1.23 other elements :(by difference).

It has been found that the Al-Fe-Si-Ti alloys of this invention are surprisingly susceptible to reinforcement by minor amounts of A1 0 particles and are also especially adapted as binders for large proportions of A1 0 particles to yield hard materials of high impact strength that have outstanding electrical properties and are strong in air to 1=2001500 C. The preparation and properties of such materials are illustrated in the following examples.

EXAMPLES XVII-XXV Various proportions of a commercial A1 0 powder (Linde A, fine abrasive) were mixed with a powder composition containiug the elements Al-Fe-Si-Ti in the proportions of 10-75-5-10 and the mixtures ball-milled as in Example I. The resultant fine powders were pressed for approximately 5 minutes in graphite dies at the pressure and temperature indicated in Table C. This table also shows the bulk density of the products and its relation to the theoretical density (assuming density of A1 0 to be 4.00 and of Al-Fe-Si-Ti alloy to be 6.50), as well as electrical and hardness properties of some of the compositions. Other physical properties are shown in Table D.

Table A Mold conditions Example Input ratio No. Raw material powders Al-Fe-Si-Ti Temp. Press. C.) (p.s.1.)

Fe, Ferrotitanium, Fe-Si alloy- 4. 0-65. 6-7. 5-22. 2 1, 260 3, 000 Fe, Ferrotitanium, Fe-Si alloy. 3. 3-72. 3-5. 8-18. 2 1, 260 3, 000 Fe, Ferrotitam'um, Fe-Si alloy- 3. 7-69. 0-6. 6-20. 2 1, 250 3, 000 Fe, Ferrotitanium, Fe-Si alloy- 4. 4-64. 7-6. 2-24. 2 1, 255 3, 000 Al, Fe, Ferrotitanium, Fe-Si 12. 4-62. 7-6. 0 18. 4 1, 230 4, 000

Sev r Sever Sev Resistivity (ohm-cm. at 25 0.)

The object was readily removed from the A specimen ing in shape to the interior of the lower portion of the crucible.

Oxidation resistance AW AD AW l AD 6 5 08611467069442 L0Z L0 0 00 0 0 O 6 Maximum impact strength (ft.1b./sq. in.)

was polished and Knoop hardness numbers determined as AW AD AW AD Oxidation resistance 1 AW AD Table B =2.s; AW= -0.2.

Table C Table D ple I. The cumulative percentage changes in linear ,204 at 1,000 g. load, 1,709 at 100 g. load, and 1,932 at Transverse rupture strength (p.s.i., l span) Bulk density (el HOT-PRESSING OF Al Oa+AlFeSiTi COMPOSITIONS Example III Transverse rupture at Strength Temperap.s.i. ture, C.

1 At 1100 C. 2 After 119 hours at 1000 0.: AD 3 At 1300 C.: AW=-0.3; AD

N 560832380 t w we? mean r m 0H0 P d w %BM%Q%MN% mn aaeaattaa e Bd S 1 505050005 m n wwaeammmm w m LLLLLLLLL n T O c w mmmmwmwwmw 9 W u 5 444434444 r P@ P t 1 9 755 321 m m tear; )5 0322015 1; wwigamm w F 7 27 7 2 7 n efiaeoeor mWA 9275563ue+ ov.+ 0 p i 0 000 0 9 m 0 1 355 7 0 1 C A m n n n n n n h H n m n n n f a nn innwv E VVIXXXXXX XXXXXXXXX and in weight (AW) after exposure to 1,000 0., 1,100 C. and 1,200 O. are

EXAMPLE XXVI The crucible was placed in a PROPERTIES OF HOT-PRESSED Al,O +AlFeSiTi COMPOSITIONS Example 4 Transverse rupture strength at higher temperatures was: 24,885 p.s.i. at 1,250 0.; 12,930 p.s.i. at 1,350" 0.; and 5,300 psi. at 1,500 C.

A mixture of aluminum, iron, silicon, and titanium the proportions (by weight) of 3% Al, 88% Fe, 3% Si, and 6% Ti was prepared by ball-milling and placed 6 1 Determined as described in Exam dimension (AD recorded.

2 Alter indicated transverse rupture test. 3 Knoop hardness after this test was 1 10 :5. load.

in an alumina crucible.

graphite tube which was then evacuated while the portion of the tube containing the crucible was heated to a temperature of about 750 C. Argon was introduced to substantially atmospheric pressure and heating cona tinued until a temperature of about 1625 C. had been Fe, Si, Ti). Although the new prodtion are composed essentially of alumiattained. This temperature was maintained for approxidiffraction patterns of the final alloys of this invention mately five minutes. During the heating no fuming of show them to be substantially devoid of the unaltered the crucible contents was observed. The assembly was free elements (Al allowed to cool and the crucible was removed from the ucts of this inven num, iron, silicon and titanium, other ingredients that do not materially affect the above-described basic and novel characteristics of the alloys of the invention can be present. Generally, the alloys will contain less than 15% (by weight) of impurities and preferably less than It is preferred that the precursor compositions contain as small amounts as possible of impurities such as C, Ca, Mn and Cr, which are usually found in minor amounts in ferrosilicon, ferrotitanium and silicotitanium alloys. Particularly is this true with respect to C and Mn which deteriorate the properties of the resultant alloy. Since the presence of manganese in the precursor compositions reduces the high temperature oxidation resistance of the alloys and objects, particularly at temperatures above about 900 C., the amount of this element should be limited to less than 5% (based on the total weight of the final precursor composition), and preferably less than 1%.

The final alloys of this invention do not contain appreciable amounts of unmodified elemental aluminum, iron, silicon or titanium, although as illustrated in the examples, these may constitute a considerable part of the precursor composition before its conversion to the alloy. This is very desirable since iron and titanium are generally not stable to high temperature oxidation, elemental silicon is brittle, and elemental aluminum is low melting.

Some oxidation of the new alloys, particularly the porous alloys may occur on prolonged heating in air at high temperature. However, such oxidation is slight as shown by the small gain in Weight and does not materially weaken the structure. In such products complex oxides may be present in minor amounts. For ease of understanding and simplicity, and since the metal ratio remains substantially unchanged, the compositions listed are those of the initial components before prolonged heating in am As indicated in the examples, the conversion of the powdered precursors to solid alloys generally involves calorescence, (i.e., an exothermic reaction characterized by an increase in temperature as evidenced by an increase in luminosity), that is induced when a considerable portion of the precursor composition is heated to a temperature of at least 900 C. The internal temperature of the shaped object during conversion is usually substantially higher than 900 C. When the spontaneous heat is small, the temperature of the externally applied heat must be higher.

As shown in the examples, the alloys of this invention exhibit desirable high temperature properties including minimum change in dimensions or weight on heating at temperatures in the vicinity of 1200" C. and high strength. In contrast, alloys prepared by the same techniques employing compositions near but outside the preferred range with respect to one or more of the elements Al, Fe, Si, or Ti, have one or more deficiencies. For example, alloys containing less than 50% Fe are deficient in impact strength and oxidation resistance and exhibit lower melting points. This is especially true when the concentration of Ti exceeds 18% without large increases in Al and Si. On the other hand, alloys containing more than 90% Fe also exhibit poor oxidation resistance at 1000 C. and have poor load bearing capacity at this temperature, although their impact strength is usually high. Concentrations of aluminum above of silicon above 9% or titanium above 25%, are undesirable because they lead to the formation of brittle alloys. Futhermore, amounts of silicon in excess of 9% tend to yield low melting phases which will cause dimensional instability at temperatures above 900 C., particularly in the 1l001300 C. range. For alloys having good dimensional stability and high impact strength, it is preferred that at most 8% Si be employed. Alloys and objects in which the concentration of Ti is less than 3% are deficient in transverse rupture strength at high tem- 10 peratures, and for good load-bearing capacity, it is preferred that at least 5% Ti be employed.

In addition to their use for conversion to shaped objects directly, the precursor compositions of this invention may also be employed in the preparation of cermets. For example, as illustrated in Examples XVII-XXV, the AlFeSiTi compositions may be mixed with aluminum oxide to give modified precursor compositions containing up to 90% A1 0 (by weight of final mixture) which, when hot pressed, yield alloys having improved strength at high temperatures. Such alloys have particularly good strength at temperatures up to about 1300 C., with some retaining their load-bearing capacity at 14001500 C. Although in firing such compositions, the aluminum oxide remains substantially unchanged, surface reaction between the aluminum oxide particles and the aluminumiron-silicon-titanium alloy may occur. This surface reaction is desirable since it promotes bonding between the phases. However, it does not appreciably modify the composition of the aluminum-iron-silicon-titanium alloy.

The properties of the alloys and objects of this invention give them utility in diverse applications. The thermal stability coupled with machinability of compositions richest in iron makes them useful in the fabrication of machine parts to be exposed to high temperature in air. The hardness of those poorest in iron makes them useful as cutting tools. These compositions and the softer alloys combined with A1 0 which are also useful as cutting tools, can be fractured into grit size and used in the preparation of bonded abrasive wheels. The electrical resistance of the alloys of this invention is in the range of conventional resistance wires and graphites and renders them useful in the preparation of electric heating elements. They may also be employed as corrosion-resistant elements in the construction of furnaces, and the like. The Al O -modified compositions of this invention are particularly valuable as load-bearing electrical elements, e.g., resistors, or even insulators if the ratio of alumina to Al- Fe-Si-Ti is above :30. Thus, aside from being electrical elements, they serve as load-bearing structures thereby permitting miniaturization.

The ease of fabrication of shaped objects is a particular advantage enjoyed by the alloys of this invention. The alloys can be made in any desired shape and their preparation is effected in air, thereby avoiding necessity for vacuum, inert or reducing atmospheres, and the products are easily made in the form in which they are to be used, e.g., as structural components of high temperature furnaces and heat engines. Moreover, the precursors of these alloys are readily available from domestic non-strategic materials.

Because of their high oxidation resistance, sintered and melt-cast alloys and shaped objects of this invention, particuarly those of high iron content, are susceptible to strength improvement by further mechanical treatments in air without protective coatings. Such treatments include the production of wrought products by forging swaging and hammering. Thus, an ingot composed of an alloy of this invention can be forged in air to produce machine parts of high impact strength.

Since obvious modifications and equivalents in the invention will be apparent to those skilled in the metallurgical arts, I propose to be bound solely by the appended claims.

The embodiments of tne invention in which an exclusive property or privilege is claimed are defined as follows:

1. Alloys and shaped objects consisting essentially of 3 15% Al, 38% Si, 6-25% Ti and the balance essentially iron, the iron being present in an amount between 60 and 88% by weight, and characterized by having good strength, dimensional stability and oxidation resistance at temperatures above about 900 C.

2. The alloys and shaped objects of claim 1 which con sists of at most 18% Ti.

3. Alloys and shaped objects having good strength in combination with dimensional stability and oxidation resistance at temperatures above about 900 C. and consisting essentially of 714% Al, 48% Si, 6-15 Ti and the balance essentially iron, the iron being present in an amount between 65-80% by Weight.

4. The alloys and shaped objects of claim 3 which consist essentially of 714% Al, 48% Si, 6-15 Ti and the balance essentially iron, the iron being present in an amount between 70 and 80% by weight. I

5. Alloys and shaped objects characterized by good strength, dimensional stability and oxidation resistancev at temperatures above about 900 C. and consisting of at least 5% of an Al-FefiSiTi alloy and up to 90% of A1 by weight, said Al-Fe-SiTi alloy component consisting essentially of 31-15% Al, 38% Si, 6-25 Ti and the balance essentially iron, the iron being present in the Al-Fe-Si-Ti component in an amount between 60-88%. 6. The alloys and shaped objects of claim wherein the Al-Fe-Si-Ti alloy component consists essentially of 20 714% Al, 4-8% Si, 6-15 Ti and the balance essentially iron, the iron being present in an amount between 70 and 80% by weight.

7. In an electrical device, an electrical component composed of an alloy of claim 5.

8. An electrical insulator composed of an alloy of claim 5 wherein the alumina is present in an amount of 70-90% by weight.

9. A precursor composition consisting essentially of 3- 15% Al 38% Si, 6-25 Ti, and the balance essentially iron, the iron being present in an amount between and 88%.

10. A precursor composition which consists essentially of A1 0 and a composition of claim 9.

11. A precursor composition consisting essentially of 714% Al, 48% Si, 6-15% Ti and the balance essentially iron, the iron being present in an amount between by weight.

References Cited by the Examiner FOREIGN PATENTS 445,614 4/36 Great Britain.

DAVID L. RECK, Primary Examiner. 

1. ALLOYS AND SHAPED OBJECTS CONSISTING ESSENTIALLY OF 3-15% AL, 3-8% SI, 6-25% TI AND THE BALANCE ESSENTIALLY IRON, THE IRON BEING PRESENT IN AN AMOUNT BETWEEN 60 AND 88% BY WEIGHT, AND CHARACTERIZED BY HAVING GOOD STRENGTH, DIMENSIONAL STABILITY AND OXIDATION RESISTANCE AT TEMPERATURES ABOVE ABOUT 900*C. 